The present invention relates to an improvement in a four-way valve for a reversible refrigeration cycle which has a comparatively small pressure receiving side constantly subjected to a high fluid pressure and a comparatively large pressure receiving side selectively subjected to a high fluid pressure and a low fluid pressure by switching action of a solenoid operated pilot valve, and constructed such that its piston or plunger moves due to the difference in effective cross sectional area between the two pressure receiving sides when a high fluid pressure is communicated to the larger pressure receiving side and due to the pressure differential when a low fluid pressure is communicated to the larger pressure receiving side.
A prior art four-way valve of the type described and actuated by a three-way solenoid operated pilot valve will be briefly described.
Referring to FIG. 1 of the drawings, the prior art four-way valve has a generally cylindrical valve body 1 which is made up of a first section 1a and a second section 1b larger in diameter than the first section 1a. Plugs 2, 3 are securely fitted by welding to the open ends of the valve body 1, respectively.
A delivery tube 5 is connected with the plug 2 to provide fluid communication between a compressor 4 and the valve body 1. A suction tube 6 is connected with the peripheral wall of the valve body 1 and leads therefrom to the compressor 4.
A tube 9 is connected with the peripheral wall of the valve body 1 to extend therefrom to a heat exchanger 7 which selectively serves as a condenser and an evaporator. Likewise, but on the opposite side to the tube 9 with respect to the tube 6, a tube 10 is connected with the peripheral wall of the casing 1 to extend therefrom to a second heat exchanger 8 which functions in the same manner as the first heat exchanger 7.
A valve member 11 is located inside the valve body 1. The valve member 11 is formed with a recess 11b in its sliding surface 11a which is calibrated such that the suction tube 6 is communicatable selectively with the tubes 9, 10 depending on the position of the valve member 11.
Valve member 11 is rigidly carried on a plunger 12 as by a rivet 13 or by brazing. The plunger 12 has a pressure receiving portion or piston A which slides within the small diameter casing section 1a and a second pressure receiving portion or piston B which is larger in diameter than the portion A and slides in the larger diameter casing section 1b. As shown, the rigid connection of the valve member 11 with the plunger 12 is located adjacent to the smaller diameter pressure receiving portion A.
The piston A of the plunger 12 defines a chamber R.sub.1 in cooperation with the casing 1 while the piston B defines chambers R.sub.2, R.sub.3 on opposite sides thereof in cooperation with the casing 1.
A solenoid operated pilot valve 14 includes a switching mechanism having a body 15. The body 15 is formed with a high pressure induction passageway 15a, a low pressure discharge passageway 15b and a common passageway 15c. A valve seat 16 having a passageway 16a therethrough is threaded into the body 15 to define a chamber R in cooperation with the body 15. Thus, the chamber R has fluid communication with the high pressure induction passageway 15a, low pressure discharge passageway 15b via the passageway 16a and the common passageway 15c. The passageway 15a leads to the delivery tube 5 through a bleed tube 17, the passageway 15b to the suction tube 6 via a low pressure discharge tube 18, and the passageway 15c to the chamber R.sub.2 in the casing 1 via a pilot tube 19.
The chamber R.sub.3 between the larger diameter casing section 1b and the larger diameter piston B of the plunger 12 is communicated with the suction tube 6 by a low pressure induction tube 20.
The pilot valve 14 has a plunger 14a from which a rod 14b extends throughout the passageway 16a of the valve seat 16. A valve member in the form of a ball 21 is received in the chamber R and actuated by the rod 14b to selectively communicate the passageways 15a, 15b with the passageway 15c as will be described.
The four-way valve constructed as above will be operated as follows. Let it be assumed that the heat exchanger 7 is located outside a desired enclosure such as a room and the heat exchanger 8 inside the enclosure.
In a cooler mode, all the components of the four-way valve and its associated pilot valve are positioned as shown in FIG. 1. The solenoid coil of the pilot valve 14 remains deenergized so that the plunger 14a is held by a coil spring 14c in a rightward position as viewed in FIG. 1. The rod 14b urges the ball 21 against the body 15 to block the passageway 15a overcoming the high pressure communicated to the passageway 15a. The passageway 16a in the valve seat 16 is communicated to the chamber R.sub.2 in the casing 1 via the common passageway 15c and pilot tube 19.
Under this condition, a low fluid pressure is admitted in both the chambers R.sub.2, R.sub.3 and acts equally on the opposite sides of the larger diameter piston B. On the other hand, a high fluid pressure is admitted in the chamber R.sub.1 defined by the smaller diameter piston A. Due to this pressure differential, the plunger 12 is maintained in its rightward position as viewed in the drawing.
Moved rightwardly together with the plunger 12, the valve member 11 causes the delivery tube 5 into communication with the outdoor heat exchanger 7 via the tube 9 while causing the indoor heat exchanger 8 into communication with the suction tube 6 via the tube 10. In this situation, fluid, i.e., refrigerant is allowed to circulate as indicated by arrows in FIG. 1 so that the outdoor heat exchanger 7 functions as a condenser and the indoor heat exchanger 8 as an evaporator.
When the coil of the pilot valve 14 is energized to switch the operation mode of the system from the cooler mode to a heater mode, the plunger 14a is attracted to the left accompanied by the rod 14b as illustrated in FIG. 2. Then, the ball 21 is urged clear of the body 15 into contact with the seat 16 by the high pressure in the passageway 15a, whereby the passageway 15a is opened and the passageway 16a closed. The high pressure is therefore admitted in the chamber R.sub.2 of the casing 1 via the pilot tube 19 so as to act on the larger diameter piston B of the plunger 12.
The pressure acting on the piston B is as high as the pressure acting on the other piston A. However, due to the difference in effective cross sectional area between the pistons A and B, the plunger 12 is moved to the left from the position shown in FIG. 1. The valve member 11 moving together with the plunger 12 reaches a position where it communicates the delivery tube 5 to the indoor heat exchanger 8 via the tube 10 and the outdoor heat exchanger 7 to the suction tube 6 via the tube 9. This sets up a fluid flow path as indicated by arrows in FIG. 2 and causes the heat exchangers 8, 7 to operate as a condenser and an evaporator, respectively.
As described above, the prior art valve causes a high pressure to constantly act on the smaller diameter piston and thereby prevents damage which would otherwise result from repeated variation in the pressure. Another advantage is that the valve member connected to the plunger can be placed in the casing simultaneously with the insertion of the plunger. However, since the plunger and valve member are formed separately from each other and then rivetted or soldered to each other, not only the assembly needs a disproportionate period of time but fixing the valve member requires a great deal of skill from the viewpoint of refrigerant flow path switching accuracy.
Because the volume of the recess formed in the valve member is smaller than that of the casing and, therefore, the resistance to the flow of a refrigerant is substantial, the casing cannot be reduced in size beyond a certain limit. To regulate the orientation of the recess in the valve member, the plunger has to be furnished with a mechanism for preventing it from being rotated about its axis.
Furthermore, where both the valve member and the plunger are made of metal, a relatively large clearance is indispensable between them and the casing to ensure a good sliding relation against any change in the temperature of the refrigerant. This frequently results leakage of the refrigerant which is detrimental to accurate switching of the refrigerant flow direction.